In 2016, i had a computer with mint on it (which is a form of ubuntu), and it was connected to an internet modem. There was a super simple gui on it that i could use to share that connection with some older hardware that were not directly connected to the internet modem. (They were not connected to the internet modem because for whatever reason, directly connecting them made them very unstable and prone to crash.) But, nevertheless, the old hardware could use the mint box with no configuration on my part, and get out to the internet through it.
Now, as it happens, i'm planning on upgrading that mint box to debian.
In preparation for that, i'm trying to share the internet with them using another box, which has debian on it, and which is connected to the internet modem. The debian box has some address like 192.168.*.* on the internet modem network, and an address like 10.*.*.* connected to the old hardware, and the two networks have no direct connection, they just both hook up to my debian machine (one on the motherboard's ethernet, and one on a usb/ethernet device).
For the old hardware, i can specify the address, a gateway, and a host for dns (all done by ip). I would choose the ip of the debian box for both the gateway and the dns, and i'd take the ip address of the old hardware to just be something unused (no need to run dhcpd on the debian box, i think).
So i just need to know what to do on the debian box so that it can field requests to get ips from host names on the internet, and forward packets to the internet modem. Hopefully, it will be some simple tool like nm-connection-editor, but maybe it has to be a series of commands. If it is a series of commands, what are they?
TIA for any info!
dan